Probing the water permeability of ROMK1 and amphotericin B channels using Xenopus oocytes.
Water permeability of ion channels in the plasma membrane of Xenopus oocytes was studied by simultaneously measuring the membrane conductance under two-electrode voltage-clamp and the cell size by video-imaging technique. The basal level of osmotic water permeability of oocyte plasma membrane was 15.9+/-0.98 microm/s (SE, n = 5). Extracellular application of pore-forming antibiotic amphotericin B at 5 microM developed macroscopic conductance of 995+/-70 microS (n = 5) and increased the osmotic water permeability of cell membrane by 44.9+/-4.1 microm/s. Meanwhile, after expressing ROMK1 channels, originally cloned from kidney, virtually no increase in the water permeability was observed even at the conductance level as high as 1113+/-47 microS (n = 5). This result suggests that even though potassium channels, like any others, are considered to be water-filled pores, K+-selective ion-transporting pathway remains virtually water-impermeable in physiological conditions, such as in kidney epithelia where huge water transport takes place at both apical and basolateral sides.
Sabirov
R Z
RZ
Department of Cellular and Molecular Physiology, National Institute for Physiological Sciences, Okazaki, Japan.
Morishima
S
S
Okada
Y
Y
D000666:Amphotericin B / Q000378:metabolism* / Q000494:pharmacology; D000818:Animals; D002463:Cell Membrane Permeability; D007473:Ion Channels / Q000378:metabolism* / Q000502:physiology; D008564:Membrane Potentials / Q000187:drug effects; D009865:Oocytes / Q000378:metabolism* / Q000502:physiology; D015221:Potassium Channels / Q000378:metabolism*; D024661:Potassium Channels, Inwardly Rectifying; D014981:Xenopus
D007473:Ion Channels; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D000666:Amphotericin B